Hypertension, or high blood pressure, affects millions of Americans and is known to be the strongest risk factor for developing cardiovascular disease. Chronic hypertension can lead to cardiac remodeling due to increased load on a patient's heart and can increase the patient's risk of developing heart failure. For about 20-30% of hypertensive patients, common pharmaceutical approaches are unable to control the rise in arterial blood pressure. For these patients, a device-based approach can be used to control blood pressure. One approach for reducing blood pressure is to target the imbalance in the autonomic nervous system often seen in hypertensive patients. This imbalance manifests as an over activation of the sympathetic nervous system and a withdrawal of the parasympathetic nervous system.
For example, muscle activation such as during postural change or exercise can cause increased sympathetic activity, thereby elevating the blood pressure. Exercise pressor reflex (neurological reflex that constricts arterioles during exercise) may raise the systolic blood pressure of a hypertensive patient to over 200 mmHg. This differs from chronic hypertension, which is marked by baseline systolic blood pressure levels above 140 mmHg. The exercise pressor reflex is particularly problematic for patients who would use exercise to improve their blood pressure. These large spikes in blood pressure can result in cardiovascular, cerebrovascular, and/or organ damage. Proper treatment requires the ability to adapt as activity levels and blood pressure fluctuates. Research into this mechanism has been conducted using fentanyl injections, which blocks sympathetic afferent nerves in the spinal cord to reduce blood pressure during exercise in heart failure patients.
In a hypertensive patient, a persistent increase in blood pressure can result in desensitization of arterial baroreceptors, which can lead to development of orthostatic hypotension. The patient experiences hypertension while in a supine position, but has orthostatic intolerance during a postural transition. This makes the treatment challenging because treating one condition could worsen the other. Such patients can benefit from a treatment option that can reduce blood pressure in a hypertensive state and increase blood pressure when the patient becomes hypotensive, such as during postural changes. For example, a therapy that reduces hypertension can be enabled during the hypertensive state and inhibited during the hypotensive state, or a therapy that heightens the blood pressure can be delivered during the hypotensive state.